There are several reasons, but I think the main one is that there is a strong bias in the hobby to dismiss any variety that is not either very obvious, or from the classic period as being little more than random variation. Indeed, within the professional circles of philately, there is a strong bias against the serious study and collection of stamps issued after World War II, dismissing them as nothing more than discount postage. Pretty well all of the professional attention in philately, especially at the exhibition level is directed towards the classic period. For Canada, the definition of the boundary between the classic and modern period has shifted with the passage of time. When I was a boy, it was the end of the Small Queen period and now it is the end of the Admiral period.
So why is there this tendency to dismiss the modern material? Part of it has to do with its availability: the stamps of issues like the Karsh and Wildings are widely available in almost perfect condition. I will say though, that they are noticeably less common than they were back in the 1980's, as usage on mail by stamp dealers has had its impact. Another reason is that classic philately has created a set of expectations and beliefs in collectors about what is considered significant and collectible, and these beliefs and expectations are slow to evolve. I'll explain further what I mean.
Most collectible varieties of the classic period result from the inherent technological limitations of the time in which the stamps were printed, such as:
- Major and minor shade varieties
- Major and minor re-entries
- Differences in paper thickness
- Plate flaws
- Differences in perforation measurement result from different perforation machines
- Wet and dry printings result from differences in the printing process
- Flat plate and rotary press printings result from different types of printing presses
- A belief that they are too common to represent a worthy challenge.
- A belief that there is little about them to warrant study.
- Inks are mixed by machines and now by computers using formulas and exact measurements resulting in very little variation in shade.
- Watermarks are no longer used because other security measures to prevent counterfeiting have superseded them.
- Engraving is no longer the main method of printing, whereas photogravure is.
- The US has employed an overall phosphorescent coating on their stamps that glows bright yellow under long wave UV and either green or orange I believe under short wave UV.
- Great Britain experimented with graphite lines in the late 1950's before adopting phosphor bands in 1959. These only react to the more dangerous short wave UV and initially they glowed green, then blue and now violet.
- Australia experimented with helecon coating in the 1950's and 1960's as well as adding helecon to inks. Helecon is a zinc-sulfide related substance that glows orange under long wave UV light. I believe that in the 1970's to the 1990's helecon was added to the papers and now they use an overall fluorescent coating.
- Nearly all the Western European countries have some kind of fluorescent coating on their stamps that was the subject of experimentation in the 1960's.
- We introduced Winnipeg tagging in 1962 that glowed bluish white under long-wave UV. This was abandoned in favour of Ottawa tagging in 1972, which glows bright green or greenish yellow. In addition some of our stamps that were printed in Australia have either a yellow or orange fluorescent coating.
- They are too expensive
- A belief that they are dangerous to the eyes
- A belief that paper fluorescence is too difficult, subjective and confusing to study